X-ray apparatus



Dec. 7, 1937. MORRISON 2,101,152

X-RAY APPARATUS Filed Dec. 24, 1931 7 v INVENTOR .RJ aw/ am Mow/50mATTORNEY Patented Dec. 7, 1937 UNITED STATES X-RAY APPARATUS MontfordMorrison, Montclair, N..J., assignor to Westinghouse X-Ray Company,Inc., a corporation of Delaware Application December 24, 1931, SerialNo. 582,933

2 Claims.

My; invention relates to X-ray apparatus and has particular relation toan apparatus for taking short exposure X-ray photographs.

It is Well recognized that in order to obtain successful radiographicexposures of short duration the X-ray. tube must be subject to heavycurrents at high potential. High tension transformers capable ofenergizing the X-ray tube with the requisite currents and potential ofsufficient magnitude would of necessity be so large that they arecommercially limited. In view of these limitations on transformers,condensers are usually employed having a capacity sufficient to permitthe storing therein of all the energy required for energization of theX-ray tube.

In the prior art systems employing condenser discharges for the takingof so-called instantaneous or short exposure radiographic exposures havebeen utilized. Such systems are, however,

defective in. practical applications due to the manner in which.discharge of the condenser takes place. In these prior systems thecondenser is charged to a predetermined amount which, when reached, isof sufiicient value to cause breakdown of a spark gap in series with theX- ray tube and condenser thus causing discharge ofthe latter throughthe X-ray tube with a re sulting radiographic exposure. 7

Systems of this type are therefore limited by the maximum capacity ofthe condenser before breakdown of theseries connected gap and noprovision for limiting the X-ray tube energization can be made otherthan the limits fixed by v the condenser itself. The resistance of thespark gap will vary with climatic conditions which changes the breakdowncharacteristic thereof.

Consequently the total amount of energy storedin the condenser will varyin accordance with. the variation in resistance of the spark-gap.Whenthe maximum energy is stored in the condenser the well known brushdischarge or leakage across the gap will occur before the completebreakdown of the gap. The leakage or brush discharge will naturally betransmitted to the X-ray tube producing X-rays before the full energy isimpressed thereupon with detrimental effect upon the radiographicpicture. Furthermore, exposures of various time periods cannot beaccomplished in a system of this type as there soris'no provision forregulating either the energy passing through the X-ray tube or theperiod of time required to discharge the condenser.

It has also been proposed to cause the discharge of a condenserdevicefor taking short ex- 552, posure radiographic pictures by maintainingthe temperature of the cathode of the X-ray tube below saturation, i.e., at a temperature below that necessary to permit electron emission ofthe cathode and to then suddenly increase this temperature toithesaturation value. This is accomplished by short circuiting a resistancein the primary. of the low tension cathode-heating transformer enablingthe temperature of the cathode to reach saturation with an attendant.discharge of the condenser. Such systems are likewise objectionable inthat an appreciable lapse of time occurs after short circuiting of theresistance in the primary winding before the cathode reaches maximumtemperature. This is due to inherent losses in the cathode heatingtransformer andthe heat inertia .of the cathodewhich is lost from theactual exposure period.

Although this time period is relatively small the discharge of thecondenser will start and gradually risewith a rise of cathode heatingtemperature resulting in a non-uniform fiow of energy from the condenserand considerable variation inthe intensity of the X-rays emanating fromthe tube.

A further unsuccessful system for taking X-ray photographs has beenproposed wherein an endeavor is made to control the flow of energythrough an electron discharge device by means of a magnetic field. Ithas been found, however,

' that due to the high potential of the X-ray circuit the magnetic fieldcannot be made sufiiciently high enough to positively prevent the fioWof energy through the discharge device and consequently the X-ray tube.Although the magnetic field will divert a portion. of the electron flowof the discharge device it will not prevent a portion of the sameflowing between the electrodes of the device.

The high potential will accordingly fiow and energize the X-ray tube aslong as the source of supply is energized. This results in theradiographic film being exposed to X-radiations of a lesser intensitywhich is merely increased by removal of the effect of the magneticfield. Accordingly as X-rays are emanating from the X-ray tube duringthe entire period that the source is energized no instantaneousradiographic exposure can result with the system being whollyinoperative for the purpose intended. In this proposed system the sourceof energy which creates the magnetic field must be completely insulatedfrom the source of high potentialenergy to prevent spark-over. Thisinsulation requirement tends to further weaken. the magnetic field andrender the system inoperative.

I have found that by employing a thermionic discharge device, such asthat shown in my copending application, filed March 5, 1932, Serial No.596,948, as a switching means in the high tension circuit I can controlthe same with minute precision. By employing a novel circuit arrangementin which the switching device is connected. in series with the X-raytube and a source of high potential heavy current energy, such as a highcapacity condenser, the discharge of the latter can be absolutelyprevented until it is clesired to take a radiographic exposure.

Furthermore by reason of the employment of a special circuit dischargeof the condenser immediately follows operation of the switching meanswith such infinitesimal time lapse as to be substantially instantaneousand both the energy supplied to the X-ray tube by the condenser and thetime period of energization of the tube can be accurately controlledwithin certain limits.

The aforementioned switching means comprises a thermionic discharge tubehaving a control electrode interposed between the anode and cathodethereof. The anode and cathode are connected to the high potentialcircuit in series with the X-ray tube and high capacity condenser andare consequently subjected to the same high potential heavy currents asthe X- ray tube. The control electrode on the other hand is suppliedwith a potential from a relatively low tension auxiliary source and bymaintaining this potential sufficiently negative relative to the cathodeof the discharge device, and the potential between the anode and cathodeI can absolutely prevent the supply of energy through the device, andconsequently from the condenser to the X-ray tube.

When it is desired to take a radiographic exposure I reverse thepotential of this low tension source from negative to positive Withoutopening this low tension source, which results in an instantaneoussupply of energy or discharge of the condenser upon consummation of thereversal of the polarity of the potential supplied to the controlelectrode. I find further that the potential of this low tension sourcewhen changed from negative to positive assists the flow of energythrough the discharge device and X-ray tube to the extent of augmentingthe energy supplied by the high capacity condenser. This particularphenomenon I attribute to the emission of secondary electrons from thecontrol electrode due to the high potential heavy current energy whichflows between the anode and cathode when a positive potential isimpressed upon the control electrode.

It is essential for satisfactory operation that the negative potentialimpressed upon the control electrode be considerably higher with respectto the cathode than when supplied with a positive potential ashereinafter more fully explained.

It should also be here stated that the polarity of the potentialimpressed upon the control electrode must for successful operation becompletely reversed without opening this source of energy. If this isnot done, but instead the potential merely made less negative or reducedto zero before being made positive by interruption of the potentialimpressed upon the control electrode, the high potential heavy currentenergy will in an infinitely short period of time build up a negativepotential on the control electrode resulting in again fblocking the flowin the same manner as when a negative potential is impressed on thecontrol electrode from the source of energy.

Heretoiore, the smallest time period in which a radiographic exposurecould be successfully taken in a practical manner has been 1/120 of asecond or during one half the wave of an alternating current cycle of 60cycles per second. With an X-ray system constructed in accordance withmy invention I am able to take exposures of infinitely short durationand as short, I believe, as 1/1000 of a second. This results in X-raypictures which disclose all portions of the human anatomy regardless ofthe fact that the same may be in motion, such as the heart and lungs.Furthermore, due to the heavy currents and high potential the varioussmall veins of the human body are clearly shown on the radiograph.

It is accordingly an object of my invention to provide a system fortaking short exposure X-ray photographs in which the energy supplied bya high potential source to the X-ray tube may be accurately controlledwith respect to time and. quantum.

Another object of my invention is the provision of a switching means inthe high tension circuit of an X-ray system which normally prevents thesupply of energy from a high tension source to the X-ray tube and whichmay be rendered operative to cause substantially instantaneous flow ofener y and to augment the same.

Another object of my invention is the provision of an X-ray system fortaking short exposure X-ray photographs employing a thermionic dischargedevice in series with the X-ray tube and source of energization which isprovided with a control electrode having a potential impressed thereuponnormally preventing the supply of energy through the discharge deviceand consequently the X-ray tube and which is adapted to assist thesupply of energy when impressed with a potential of opposite polarity.

A further object of my invention is the provision of a system for takingshort exposure X-ray photographs in which the energy for supplying theX-ray tube is taken from a condenser and in which the supply of energytherefrom is controlled with minute precision with an entire absence oftime lag.

'Still further objects of my invention will become apparent to thoseskilled in the art by reference to the accompanying drawing in which .1esingle figure is a diagrammatical representation of a system for takingshort exposure X-ray photographs showing one form which my invention maytake.

Referring now to the drawing in detail I have shown a source ofcommercial alternating potential, such as a generator 5. An autotransformer i3 is connected to this source by means of a pair ofconductors l and 8. This auto transformer in turn is arranged to supplyenergy to the primary winding 9 of a high tension transformer 50, bymeans of a pair of conductors l2 and 13, when a hand operated switch 54is closed to complete the conductivity of the conductor 13. Theconductor 52 may connect to an adjustable arm of the auto-transformer,if desired, in order to vary the voltage supplied to the high tensiontransformer 10.

The secondary winding !5 of the high tension transformer 15 is connectedto the cathode of a rectifying valve tube M3, by means of a conductorif, and to the anode end of a similar valve tube it, by means of aconductor I9.

The anode of the valve tube 16 is connected,

by means of a conductor .20, to a condenser 22 andthe cathode of therectifying valve [8 is similarly connected, by means of a conductor. 23,to a condenser device 24. These condensers 22 and 24 are in turninterconnected by means of a con-'- ductor v25, which is suitablygrounded at 26. A conductor. 2'! interconnects these two condensers withthe mid-point of the secondary winding l5 of the high tensiontransformer I0. This limits the insulation requirements of the highpotential system to one-half the total output energy of this secondarywinding I5. The portion of my system thus far described is adapted tostore relatively heavy currents at high potential in the condenserdevices 22 and 24.

Although I have shown two condensers 22 and 24, respectively, and tworectifying valves l6 and I8 it can be appreciated that one condenser andone valve tube would just as readily sufiice. However, should a singlecondenser be utilized in place of the two condensers as shown thecapacity of the same would necessarily have to equal that of the two.Furthermore, in the appended claims it is to be understood that thesameare to be interpreted as including the use of a single condenser andvalve tube as well as the preferable form hereinabove described.

An X-ray tube 28 has its cathode end connected to the conductor 20 andcondenser 22, by means of a conductor 29, and the anode end of a threeelectrode electron discharge device is similarly connected to theconductor 23 and condenser 24, by means of a conductor 32.

The cathode of the discharge tube 30 and anode of X-ray tube 28 areconnected together by means of a conductor 33. The thermionic cathode ofthe X-ray tube 28 is arranged to receive low tension heating currentsfrom a heating transformer 34, the primary of which is connected to theconductors I and 8 extending from the source of supply 5, by means of apair of conductors and 35.

A variable resistance 31- is connected in series with one ofthese'conductors, 36 for instance, for the purpose of regulating thecathode heating temperature of the X-ray tube. The thermionic cathodesof the rectifying valves I6 and I8 and electron discharge device 30 arelikewise arranged to receive heating currents from a source of lowtension supply, such as batteries or low tension transformers 38, whichlikewise may have their primary windings connected to the sourceofsupply 5 in the same manner as that of the transformer 34.

The discharge device 30 in addition to its anode and cathode is providedwith a control electrode in the form of a grid interposed between theanode and cathode. This control electrode is adapted to have a suitablepotential from an auxiliary source impressed thereupon which is normallyof suflicient magnitude to prevent the supply of the energy stored inthe condensers 22 and 24 between the anode and cathode thereof, andconsequently through the X-ray tube 28. This auxiliary source ofpotential comprises a circuit similar to that of the high voltagecircuit, namely a transformer 42, having its pri mary winding 43connected by means of a pair of'conductors 44 and 45 to the conductors Iand 8 extending from the source 5.

A secondary winding 46 has one of its ends connected to the anode of therectifying valve 41 and the cathode end of av similar rectifying valve48 by means of a conductor 49-. The cathode end iIthe, rectifyingvalve41 isconnected, by means.

of a conductor 50, to a condenser 52 with the anode end of therectifying valve 48 connected, byv means of a conductor 53, to acondenser 54 and the opposite end of the secondary winding 46-isconnected to a conductor 55, whichinterconnects the condensers'52 and54.

The cathodes of the respective-rectifying valves 41 and 48 are adaptedto receive heating currents from a suitable source of energy 56 in thesame manner as previously described relative to the sources 38. Thisportion of the auxiliary source of potential is arranged to store energyduring each half wave of the alternating current cycle in the respectivecondensers 52 and 54' which are arranged to discharge through an outputcircuit which comprises a pair of conductors 51 and 58 connected to aplurality of resistance elements 59, and 62. These respective resistanceelements are connected in the form of a Wheatstone bridge circuit withthe conductor 58 connected to one end of the respective resistanceelements 60v and 62 and the conductor 51 connected to one end of theresistance element 59. A conductor 63 connects one end of the resistanceelement 62 to the control element of the discharge device'30 and asimilar conductor 54 connects one end of the respective resistanceelements 59 and 60 to the conductor 33 and consequently to the cathodeof discharge device 30.

Apair of contact terminals 65 are interposed between one end of theresistance elements 59 and 62 which terminals are normally open butwhich are adapted to be bridged by means of a relay 66. This relayreceives energization from a small insulating transformer 61, theprimary of which is connected by means of a pair of conductors 58 and 69extending to the conductors I and 8 constituting the commercial sourceof supply. The conductor 68, however, is providedwith a pair of contactterminals disposed adjacent the aforementioned hand switch l4 and arethus adapted to be bridged by the same, as hereinafter more fully setforth.

The resistance elements 59, 50 and 62 constituting the Wheatstone bridgecircuit each have equal ohmic resistance although it is not essential inevery instance that their resistance be of equal ohmic value. Theseresistance elements are connected to the control'electrode in such amanner as to constitute a polarity reverser as hereinafter more fullyexplained. At the operating potential of the X-ray tube, in theactualembodiment of the apparatus which I have constructed, I have found thatthe total output energy of the condensers 52 and 54 should beapproximately 8000 volts in order to completely block or preventdischarge of the high voltage condensers 22 and 24. When the system isin the position as shown in the figure a negative potential of one-halfthe output of the low potential system is impressed upon the grid of thedischarge device 30, or -4000 volts, which is of a sufficient magnitudeto prevent the flow of the energy from the condenser. devices 22 and 24through the discharge device 30 and X-ray tube 28.

Although I have found that this negative potential' as above noted issuiiicient to block the flow in the high potential circuit with thepotenmust be higher or lower with the ratio therebetween substantiallythe, same.

The control electrode of the discharge device 30 now being operative toprevent the discharge of the high potential energy through the X-raytube is then rendered operative to permit the substantiallyinstantaneous flow and assist the same by closure of the relay 66. Thisestablishes a diiferent circuit by which the polarity of the potentialimpressed upon the control electrode of the discharge device 30 isreversed although this potential is of a slightly less magnitude due toan unbalanced condition of the resistance elements constituting theWheatstone bridge circuit.

The operation of my system may be best understood from a given mode ofoperation. Assuming, therefore, it is desired to take a short exposureX-ray photograph, the cathode heating temperature of the X-ray tube 28is set, by means of the variable resistance 31, to the desired electronemissivity. The hand switch I4 is then moved to the left completing theconductivity of the conductor i3 and energy will therefore flow from theauto transformer 5 to the primary winding 9 of the high tensiontransformer ID. The voltage supplied to the primary winding 9 isregulated by means of the adjustable arm of the auto-transformer towhich the conductor i2 is connected to the desired potential. Thesecondary winding l5 causes energy to flow through the respective valvetubes l6 and l8 to the condensers 22 and 2 during alternate half wavesof the alternating current cycle.

This circuit may be traced from the secondary winding 5 5 by means ofthe conductor I! through the rectifying valve l6, conductor 29 to thecondenser 22 and thence back to the secondary winding by means of theconductors 25 and 21. In a similar manner current will flow by means ofthe conductors 21 and 25 to the condenser 24 and thence back to thesecondary winding by means of the conductor 23, rectifying valve 18 andconductor l9.

Although strictly speaking the current does not flow through thecondensers 22 and 24 it can be appreciated that energy will be stored ineach of the respective condensers during alternate half waves of thealternating current cycle in the manner as just described, until thesame are completely charged with heavy current at a high potential to apredetermined maximum value depending upon the setting of theauto-transformer. Discharge of absolutely any of the energy stored inthe condensers, however, through the output circuit comprising thedischarge tube 39 and X-ray tube 28 is at this time prevented by theaforementioned action of the control electrode of the discharge tube andthere is no leakage through the X-ray tube which would tend to delay thecondensers in being charged to their predetermined maximum value or thegeneration of any X-rays of even a Weak intensity. The condensers 52 and54 will accordingly impress a sufficient negative potential upon thiscontrol electrode through a circuit which may be traced from thecondenser 58, which is negatively charged, by means of conductor 58 toone end of each of the respective resistance elements 55 and 62, wherethe circuit divides, a portion thereof extending through the resistanceelement 62 to the control electrodeof the discharge device 3!), thusimpressing a negative potential equal to onehalf of the total of theoutput circuit thereupon. The remainder of the circuit extends throughthe resistance elements 69 and 59 back to the condenser 52 by means ofthe conductor 51.

The conductor 64 connects one end'of the respective resistance. elements59 and BI] to the cathode end of the discharge device 30 and thereforeimpresses a zero potential upon the cathode which is positive relativeto that of the control electrode, the latter as aforementioned nowcarrying a large negative potential. This'becomes readily apparent whenit is appreciated that the voltage drop through the series connectedresistance elements 59 and 66 is equal due to their ohmic resistancebeing the same. The conductor 34 being connected to the midpoint betweenthese two resistance elements therefore is at zero potential withreference to the source. The resistance element 62 on the other hand isnot connected directly in the circuit and as there is no current flowingtherethrough a negative static potential is impressed upon the grid.

Assuming now that everything is in readiness to take a radiographicexposure the hand switch I4 is moved to the right, as shown in thefigure, thus opening .the circuit to the primary winding 9 and closingthe circuit from the commercial source of potential to the primarywinding of the insulating transformer 61. Energization of this windingwill energize the winding of the relay 66 and cause the same toestablish contact with the contact terminals 65 which constitute theremaining leg of the Wheatstone bridge circuit. Closure of this relayinstantaneously reverses the polarity of the potential impressed uponthe control electrode of the discharge device 30 without opening thecircuit or permitting any electrical phenomenon to interfere with thesimultaneous discharge of the high tension heavy current energy storedin the condensers 22 and 24 through the discharge device 30 and X-raytube 28.

Upon closure of the relay 66 positive potential will be impressed fromthe condenser 52 which is positively charged, through the conductor 51,contact terminals 65 and thence through conductor 63 to the controlelectrode of the device 30. At the same time a current will flow throughthe series connected resistance elements .59 and 69 in the same manneras previously described when a negative potential was applied to thecontrol electrode. However, as the control electrode of the dischargedevice 39 is now positive relative to the cathode and the latter isnegative a current will flow between the cathode and control electrodeforming a circuit which naturally has an inherent ohmic resistance.

This circuit is equivalent to connecting an ohmic resistance in parallelwith the resistance element 59 which operates to create an effectanalogous to that of lessening the ohmic resistance of the latter andrender the same no longer equal to the ohmic resistance of the element69. This will therefore cause a greater voltage drop across theresistance element 60 than across the resistance element 59, resultingin a lesser value in the positive potential impressed upon the grid thanwhen a negative potential was previously impressed thereon. Thepotential at the midpoint between the respective elements 59 and 69, towhich the cathode of the discharge device 30 is connected is now nolonger at zero relative to the source but is carrying a potential. Thispotential, therefore, is impressed upon the cathode but not being ashigh as that impressed upon the grid enables a current to flow throughthe filament grid circuit comprising the resistance element 59. The highvoltage energy therefore instantaneously flows between the anode andcathode without any variation or'gradualrise simultaneously with thechanging of the potential impressed upon the control electrode fromnegative to positive so that the energy initially supplied to the X-raytube by the condensers 22 and 24 is at its predetermined maximum value.

The capacity of the condensers 52 and 54 are such that a constantpotential of the desired polarity is always impressed upon the controlelectrode of the discharge device 30. The operation of my system thusfar described is based on the assumption that the cathode of the X-raytube 28 was heated to its maximum intensity which permits instantaneousflow of the energy from the high potential source upon reversal of thepolarity of the control electrode. When,

however, a radiographic exposure is desired of longer duration or oflesser energy output the temperature of the cathode is merely lowered bymeans of the adjustable resistance 31 in the cathode heating circuit andthe energy stored in the condensers 22 and 24 isregulated by theauto-transformer 6.

Furthermore, it should be here noted that the switch [4, when operatedto affect reversal of'the potential impressed upon the control electrodeof the discharge device 30, first interrupts the supply of energy to theprimary winding 9 of the high tension transformer thus interrupting thecharging of the high potential condensers 22 and 24 after they have beencharged to their predetermined maximum value. This accordingly divorcesthese condensers and consequently the X-ray tube excitation circuit fromthe alternating current and condenser charging circuit prior to thedischarge of the condensers. The result, therefore, is an entire absenceof a sinusoidal ripple in the X-ray tube excitation current whichapplicant believes is a contributing factor of considerable import tothe resulting phenomenon producing apparently X-rays of novelcharacteristics.

It can, therefore, be readily seen that I have provided an X-ray systemfor taking instantaneous X-ray photographs in which current flow in thehigh potential circuit is positively prevented by means of a thermionicdischarge device provided with a control electrode. By impressing anegative potential upon this electrode of sufficient magnitude the hightension heavy current is completely blocked and upon reversal of thispotential from negative to positive instantaneous energization of theX-ray tube simultaneously occurs without variation in energy suppliedthereto and consequently a uniform intensity of X-rays emanating fromthe X-ray tube results.

Furthermore, the circuit which in one instance impresses a negativepotential upon the control electrode and in the other instance impressesa positive potential thereupon is not opened during the reversal of thispotential.

In consequence of this no electrical phenomenon can occur which isdetrimental to the successful instantaneous energization of the X-raytube. The latter does not become energized nor is any energy suppliedduring the switching operation and not until the complete consummationof reversal of the polarity impressed upon the control electrode.

Although I have shown and described one specific embodiment of myinvention I do not desire to be limited thereto as various othermodifications of the same may be made without departing from the spiritand scope of the appended claims.

What is claimed is:

1. In an X-ray system for taking X-ray photographs in a short intervalof time, the combination with an energy storage means connected to asource of rectified alternating current energy for accumulating anelectrical charge in said energy storage means, and an X-ray tubeconnected to said energy storage means and adapted to be energized bythe charge accumulated therein, of a thermionic discharge deviceinterposed between said energy storage means and said X- ray tube forcontrolling energization of the latter, an auxiliary source ofelectrical energy connected to one of the electrodes of said dischargedevice normally operative to impress a potential thereupon to preventenergization of said X-ray tube and adapted to reverse the polarityimpressed upon the discharge device to cause energization of said X-raytube by the accumulated charge, and means associated with said auxiliarysource and said rectified alternating current source, and operable toreverse the polarity of the potential impressed by said auxiliary sourceupon one of the electrodes of said device to render said dischargedevice effective to cause energization of said X- ray tube by theaccumulated charge and to interrupt the accumulation of a, charge insaid energy storage device to prevent the imposition of a sinusoidalwave form upon the X-ray tube excitation energy.

2. In an electrical system, the combination with a load, a source ofhigh potential electrical energy therefor, and a high potential switchinterposed between said load and said source provided with an anode, acathode, and a control electrode, and operative to cause and prevent theenergy from said source to be supplied to said load, of means forsupplying a potential to the control electrode of said high. tensionswitch to cause and prevent the energization of said load by said hightension source comprising a source of electrical energy connected to thecontrol electrode of said high tension switch, a plurality of resistanceelements interposed between said last mentioned source and the controlelectrode of said high tension switch and operative to normally causesaid source to impress a negative potential upon said control electrodeto render the same effective to cause said high potential switch toprevent energization of said load by said high potential source, and aswitch associated with said resistance elements and operable to cause areversal in the polarity of the potential impressed by said lastmentioned source upon the control electrode of said high tension switchfrom negative -to positive without interrupting the supply of thepotential impressed upon said control electrode to cause said hightension source operation of said last mentioned switch.

MONTFORD MORRISON.

